Error out on send failure in walsender loop.
Error out on send failure in walsender loop.

I changed the loop in 9.3 to use "goto send_failure" instead of "break" on
errors, but I missed this one case. It was a relatively harmless bug: if
the flush fails once it will most likely fail again as soon as we try to
flush the output again. But it's a bug nevertheless.

Report and fix by Andres Freund.

adam8157/gpdb,techdragon/Postgres-XL,oberstet/postgres-xl,lisakowen/gpdb,ashwinstar/gpdb,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,pavanvd/postgres-xl,jmcatamney/gpdb,adam8157/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,ovr/postgres-xl,greenplum-db/gpdb,techdragon/Postgres-XL,ashwinstar/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,Postgres-XL/Postgres-XL,ashwinstar/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,oberstet/postgres-xl,yazun/postgres-xl,ovr/postgres-xl,xinzweb/gpdb,yazun/postgres-xl,Postgres-XL/Postgres-XL,adam8157/gpdb,50wu/gpdb,lisakowen/gpdb,techdragon/Postgres-XL,Postgres-XL/Postgres-XL,xinzweb/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,techdragon/Postgres-XL,yazun/postgres-xl,jmcatamney/gpdb,jmcatamney/gpdb,oberstet/postgres-xl,zeroae/postgres-xl,jmcatamney/gpdb,ashwinstar/gpdb,oberstet/postgres-xl,ashwinstar/gpdb,Postgres-XL/Postgres-XL,pavanvd/postgres-xl,zeroae/postgres-xl,xinzweb/gpdb,ovr/postgres-xl,greenplum-db/gpdb,yazun/postgres-xl,jmcatamney/gpdb,50wu/gpdb,ashwinstar/gpdb,adam8157/gpdb,xinzweb/gpdb,lisakowen/gpdb,pavanvd/postgres-xl,greenplum-db/gpdb,50wu/gpdb,adam8157/gpdb,xinzweb/gpdb,ovr/postgres-xl,jmcatamney/gpdb,lisakowen/gpdb,jmcatamney/gpdb,zeroae/postgres-xl,greenplum-db/gpdb,adam8157/gpdb,Postgres-XL/Postgres-XL,lisakowen/gpdb,ashwinstar/gpdb,lisakowen/gpdb,50wu/gpdb,techdragon/Postgres-XL,50wu/gpdb,oberstet/postgres-xl,50wu/gpdb,pavanvd/postgres-xl,yazun/postgres-xl,adam8157/gpdb,pavanvd/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl,adam8157/gpdb,ovr/postgres-xl